For no particular reason, here’s a bit of history about the offside law.
Back in 1972 former referee Ken Aston wrote a regular column in the Arsenal programme, which in those days contained 16 pages and was priced at a princely 5 pence. On 2 September, Ken’s column discussed a proposed change to the offside law, whereby you could only be offside when within your opponents’ penalty area. This was trialled in the Anglo-Italian Cup, the Watney Cup and then the Metropolitan London League for the first half of the season. Ken seemed quite keen on the experiment – not necessarily keen on the change, that had to be proven to be a good thing before he’d get enthusiastic – but he was keen to try. 
Whether the experiment lasted any longer than the initial trial period up to Christmas 1972, I don’t know for sure, but the Sunday People reported in early December that it was ‘a flop’ and would probably be abandoned. Obviously it was never implemented any wider.
Interestingly, though, three months before Ken’s column appeared in the Arsenal programme the North American Soccer League, then in its fifth season, changed the offside law it was using and on June 26th introduced the 35 yard offside line that was retained until the league folded in 1984.
Somehow my memories of the NASL are all in technicolor, while the black and white Arsenal programme and picture of Ken Aston look as though they’re from the time of post-WW2 rationing. Amazing that the NASL made their change before the Metropolitan London League experiment.
The NASL weren’t first with the idea though – in 1925 the FA arranged three experimental games where the teams played 45 minutes with a 40-yard offside line and the other 45 with two defending players needed between attacker and goal rather than three (the latter being the law at the time). They decided reducing from three to two players was a better idea than moving the area that offside applied to, and the rule was changed. Herbert Chapman invented the WM formation as a result, Arsenal became the biggest club in the world (for a while) and the rest is history.
There’s an interesting (though not 100% accurate – see comments) history of the offside law (and why it’s ‘a work of genius’) from The Guardian here.
Ken Aston had an interesting career himself. He was the first ref to wear black uniform with white trim, refereed the infamous ‘Battle of Santiago‘ at the 1962 World Cup, and invented the system of red and yellow cards. Read about him here.
angryofislington 
Funny that, I thought along similar lines recently, with regards to the off-side rule. Totally ignorant of the history you have described above. My thought was to extend the line of the penalty area to the edges of the pitch (similar to the above), but to have no offside if, A,- the ball is taken into this area by the opposition, or B,- the ball is won back from the defending side within this area. Any ball launched straight into that area and received by the attacking side would deemed to be offside. However, having read your stuff I see a problem with my idea for attacking midfielders, who, like Alex Song for example, are quite adept at chipping the ball over the top from further out? However, moving the line further up the pitch might give too much advantage to the attacking side? Back passing from out of the area would not be a problem, as it would put attackers onside. For the officials it would be much more simple though. Only two questions need to be asked before declaring a player offside -1, If the ball is played into this area by the attacking side, who touches the ball first? Attacker – offside. Defender – attackers now all onside. Or -2, Was the ball played outside of this area, or carried into the area by the attacking side? A lot easier than trying to judge who was ahead of who when the ball is played? The assistant can decide on question 1, being ahead of play, and the referee question 2 as he would be in that vicinity. It might be worth a trial don’t you think?
Time for a bit of pedantry!
There are some errors in the Guardian article.
It says that Newcastle’s sixth 0-0 draw of the season in February 1925 was the final straw and that an experimental game was then played.
Well, there were three experimental games played and they were played on 31 January 1925 (i.e. before the Newcastle v Bury game).
If you’re going to be innovative, then you ask the game’s great innovaters to take part. So, Arsenal was one of the teams involved. Being knocked out of the FA Cup in the first round also helped. They played a game against Chelsea at Highbury. In the first half they used the 40 yard rule and in the second half they used the two defenders rule. It didn’t exactly result in an avalanche of goals (Chelsea won 1-0) but the game flowed much better.
The other two games finished Orient 1 Wolves 1, and Charlton 3 Luton 1.
As usual, thanks for the extra info Andy.